Air intake filter and silencer



June 6, 1950 c. G. VOKES AIR INTAKE FILTER AND SILENCER 2 Sheets$heet 1 Filed Dec. 20, 1948 Attorney June 6, 1950 c, vo s 2,510,441

AIR INTAKE FILTER AND SILENCER Filed Dec. 20, 1948 2 Sheets-Sheet 2 F/GZ.

Invenlor Attorney Patented June 6, 1950 AIR INTAKE FILTER AND SILENCER Cecil G. Vokes, Guildford, England, assignor to Vokes Limited, Guildford, England Application December 20, 1948, Serial No. 66,347 In Great Britain December 29, 1947 3 Claims. 1

In application Ser. No. 705,554 there is described an intake silencer in which the entering air passes first through a zone of high frequency elimination, next through a low frequency silencer (preferably including a resonator designed for the dominant sound) and finally through a fibrous or other sound absorbing filter. The result is that the sound waves emerging from the engine or other intake first pass through the filter, then the low frequency silencer and finally the high frequency elimination zone where there is an induced suction effect.

The illustrated form shows the air inlet in the side of a cylindrical casing so that the air enters radially between two tubes of difierent length, of which one is a low frequency resonator and the other leads into a domed end cap, forming a suction zone, and perhaps also a shorter resonator.

It has been found in practice that better results are obtainable in some cases by locating a domed or conical baflle or reflector with its open end opposite to the inlet end of the low frequency tube, but of greater area than the tube, so that it helps to absorb low frequency noises issuing from the tube. The air is admitted to the apparatus at the end outside the reflector, so that the entering air flows past the outside of the reflector in an annular space preferably of substantially con stant cross-sectional area and then turns inwards into the high frequency zone and thence through the low frequency resonator.

It is also found preferable to provide the apertures in the resonator near its inlet end, leading directly into the zone (where the pressure is slightly lower) inside the filter and helping in distribution of air over the full length of the filter.

An alternative method of air flow to each end of the filter is to permit an aperture approximately half way down the centre tube, and to cover the aperture with a, tube of larger diameter having its open end at the front and blanked off at the rear behind the aperture. In this way the maximum length of the acoustic tube is maintained when measured in either direction.

The silencer is in other respects like that described and the present invention provides these improvements or modifications.

A typical form is shown upon the accompanying drawings whereof:

Fig. 1 is a central longitudinal section, and

Fig. 2 is an end view.

The combined filter and silencer shown has a main body part comprising a central resonator tube I and concentric outer case 2. A cap 3 contains a concentric domed bafile or reflector 4 with its open end facing the inlet of the tube I. Thecap 3 and a partition 5 are secured to the case 2 by beading 6, leaving a high frequency elimination zone I between the tube I and the dome 4. Apertures 8 are provided near the inlet end of the resonator tube I to assist in the distribution of fiow to the filter element I5.

A closure cap 9 is fitted to the outer case so that the air turns back into the annulus between the central tube and outer case. The closure cap 9 may be secured by a wing-nut I0 engaging a threaded rod II carried by a cross bar or spider I2 at the end of the tube I. Felt or like discs I3, I4 are fitted inside the partition at the far end of the annulus and in the closing cap respectively and make joint with the ends of the tapered star-shaped or deeply pleated filter unit. A retaining clip IS with tightening screw 20 can also be fitted to the outer case.

Air entering the apparatus at the inlet end of the cap 3 flows through the annular space 2|, of substantially constant cross-sectional area, surrounding the dome 4, before turning inward and entering the high frequency elimination zone I and resonator tube I. The air which has passed into the tapered annular space I! inside the element will emerge through the filtering material into a reversely tapered annular space I8 outside it and communicating with a lateral branch I9 which forms the outlet for the filtered air from the combined filter and silencer to the engine intake.

Either tube or casing may advantageously be tapered in some cases.

Other suitable forms of filter unit may be used within the wider aspects of the invention, for instance a brush type.

It will be noted that the emerging sound waves pass through the sound absorbing material of the filter before passing through the low frequency chamber or resonator and then through the zone where exposure to a chamber in which a partial vacuum is induced has the well-known tendency to level out the high frequency waves.

I claim:

1. A filter and silencer assembly comprising an elongated casing closed at one end and having a substantially central opening of reduced dimensions at the other end, an inlet end portion extending axially from the latter end of said casing and having an end located inlet substantially aligned with said opening, a tubular member longitudinally in said casing and connected thereto at one end in communication with said opening and having an outlet at the other end that opens into said casing, said member defining a low frequency silencing chamber and cooperating with said casing to define an annular filter chamber, a substantially cylindrical filter element extending longitudinally in said casing between the ends thereof and surrounding said tubular member to divide said filter chamber into concentricsections, an outlet in theside of said casing and opening laterally from the outer of the filter sections, and a domed reflector con-- centrically in said inlet end portion and-spaced therefrom to define an annular inlet passage therebetween, said reflector b'eing spaced from the adjacent casing end to define a high fre quency elimination zone andhavingxan opening on its inner side opposite said casing openingiand of greater area than said casing opening to promote a reduced pressurewithin said refie'ctoFfor modifying the high frequency waves.

Z J- A n assembly 'a's'defined in -c1ain'1 1 wherein said tubular member comprises: a 'ertures"open: ing laterally' into said filter-chamber adjacent" its' connection' withsaid'casing;

3. An assembly as defined in claim 1 wherein said inlet end portion is slightly domed and spaced from said domed reflector to cooperatively provide said annular inlet passage with a substantially constant cross-sectional area to enable an even inlet flow.

CECIL G. VOKES.

REFERENCES CITED The following references are of record in the file of this patent:

STATES PATENTS 

